1. Field of the Invention
The invention relates to a thermal relay comprising a plurality of bi-metallic strips housed in a first cavity of a case and heated by currents from a multi-phase network which feed a load, and which flow through a separate electromagnetic contactor placed in series, these bi-metallic strips acting, when these currents exceed a certain threshold for an extended period, on a quick break switch placed in series with the coil of the contactor and, on the other hand, means for transmitting and selecting the operating mode of this switch between two quick break working modes, one of which is provided with automatic re-make and the other with manual re-make, this switch and these means being placed in an electromechanical sub-assembly adapted for being housed in a second cavity of the case.
2. Description of the Prior Art
Such thermal relays which are widely used in circuits feeding multi-phase motors, whose protection they ensure should extended overloads appear, may be illustrated by the French patent No. 2 536 906 of the Applicant.
In this known apparatus, whose size and function do not necessarily imply that it is incorporated in a complex automated system, a single switch is disposed in a removable sub-assembly.
It is known that, in some known thermal relays, a second quick make switch is associated with the transmission means which actuate the break switch so as to show the appearance of a fault through its incorporation in a signalling circuit which is electrically independent of the one concerning the coil of the contactor.
If it is desired that such a signalling function is accomplished by an electromechanical sub-assembly such as the one defined above, its volume is necessarily increased and the problem arises of not overloading the transmission mechanism so as to preserve its sensitivity properties which constitutes its advantage. It is moreover frequently required that the electric signalling, which may be communicated remotely through conductors of great length, is accompanied by local optical signalling which also shows the appearance of a fault, and that local manual control means are provided for checking the correct operation of the switch or switches by mechanically simulating the appearance of a current fault.